Wednesday, November 25, 2015

Carl Zimmer in the New York Times summarizes recent results from a wide ranging study which incorporates the genetics of extant as well as ancient Europeans. The study found evidence for several instance of natural selection altering height, digestion, skin color and our immune system.

Previous studies had suggested that Europeans became better able to digest milk once they began raising cattle. Dr. Reich and his colleagues confirmed that LCT, a gene that aids milk digestion, did experience intense natural selection, rapidly becoming more common in ancient Europeans. But it didn’t happen when farming began in Europe, as had been supposed. The earliest sign of this change, it turns out, dates back only 4,000 years.

While agriculture brought benefits like a new supply of protein in milk, it also created risks. Early European farmers who depended mainly on wheat and other crops risked getting low doses of important nutrients.

So a gene called SLC22A4 proved advantageous as soon as Europeans started to farm, Dr. Reich and his colleagues found. It encodes a protein on the surface of cells that draws in an amino acid called ergothioneine. Wheat and other crops have low levels of ergothioneine, and the new variant increases its absorption. That would have increased the chances of survival among the farmers who had the gene.

People who are followers of the going back to a hunter gatherer Paleolithic diet fad, take note. Our digestive arsenal and our micro-biomes have responded to a different agricultural food combination. Human evolution did not freeze with the coming of the ice age. Agriculture and animal domestication have pushed evolution into changing our DNA.

Saturday, November 21, 2015

Homo floresiensis is an extinct, diminutive hominin species discovered in the Late Pleistocene deposits of Liang Bua cave, Flores, eastern Indonesia. The nature and evolutionary origins of H. floresiensis’ unique physical characters have been intensively debated. Based on extensive comparisons using linear metric analyses, crown contour analyses, and other trait-by-trait morphological comparisons, we report here that the dental remains from multiple individuals indicate that H. floresiensis had primitive canine-premolar and advanced molar morphologies, a combination of dental traits unknown in any other hominin species. The primitive aspects are comparable to H. erectus from the Early Pleistocene, whereas some of the molar morphologies are more progressive even compared to those of modern humans. This evidence contradicts the earlier claim of an entirely modern human-like dental morphology of H. floresiensis, while at the same time does not support the hypothesis that H. floresiensis originated from a much older H. habilis or Australopithecus-like small-brained hominin species currently unknown in the Asian fossil record. These results are however consistent with the alternative hypothesis that H. floresiensis derived from an earlier Asian Homo erectus population and experienced substantial body and brain size dwarfism in an isolated insular setting. The dentition of H. floresiensis is not a simple, scaled-down version of earlier hominins.

Monday, November 16, 2015

These are the twin pinnacles of Tail Baila, a popular trekking spot near the Western Ghat escarpment about 100 km west of Pune. I get asked often whether Tail Baila is a volcanic plug or a dyke. It is neither. The pinnacles are lava flows. There is a strong structural control over erosion in this part of the Deccan Volcanic Province. Take a look at the satellite imagery below.

I have marked in orange arrows, a strong roughly N-S oriented fracture system. In yellow arrows is a less prominent E-W oriented fracture system. The white dotted line is the Western Ghat Escarpment. These fracture systems have their origins in the tensional forces that broke apart fragments of Gondwanaland, with the Indian continental block separating from Madagascar around 88 mya and Seychelles breaking off from the Indian block about 66 mya. The latter rifting event coinciding with India drifting over a hot portion of the mantle known as the Reunion hotspot also triggered Deccan volcanism. Many of these fractures acted as conduits for magma to rise to the surface and spread as massive lava flows. Magma still occupies some of these fractures. These clogged up pipes are called dykes.

A paleo-geographic reconstruction of India in relation to other Gondwana continents and Asia during Deccan volcanism 66 million years ago is presented below.

The legacy of these ancient tensional gashes didn't end with Deccan volcanism but has influenced the evolution of the landforms we see today. Since the lava pile is fractured, physical weathering -aided by water seepage, disruption by plant roots and by temperature changes- peels off slabs of lava along these weak fractures faces. Rock falls are a common site at the base of many cliffs. Removal of blocks of lava eventually results in the formation of isolated mesas, buttes and pinnacles, remnants of once continuous lava flows. Streams follow narrow fracture zones and carve out steep sided canyons. The result, after eons of weathering and erosion, is a spectacular landscape with plateaus, narrow valleys, high basalt cliffs and pinnacles shaped as rectangular blocks like Tail Baila.

Update- November 17 2015: Since this topic is of great local interest let me add another thought. The Western Ghat escarpment also has been undergoing this type of physical weathering and erosion along cracks and fractures. The original location of this escarpment would have been tens to a hundred km west of the present line. For millions of years the escarpment has been retreating eastwards as lava blocks have peeled off the cliff face. The Deccan Plateau was much wider in the past. It is being eaten up by eastward erosion. Places similar to Tiger's Leap and Konkan Kada would have been to the west earlier in geological time!

Last Sunday I drove with some friends on one of the loveliest back country roads in this part of the country. The interactive map below shows the route looping around the backwaters of the Mulshi Dam from village Valane to village Nive.

A gnarly trunk of the Peepal tree with the Mulshi backwaters

Thick lava flows of the Deccan Traps with crude columnar jointing.

In a distance a pretty colorful entrance to a temple is glimpsed through the trees.

Serene backwaters

A lonely stretch of road through a woodland...

opens up with vistas of grasslands, upland forests and high basalt cliffs

Throughout the Holocene this tug of war has continued... where farmland meets forest.

Distant pinnacles shimmer in the afternoon haze

When I was in college, geology was a road less traveled by. I am so glad I took it.

The claims of periodicity in impact cratering and biological extinction events are controversial. A newly revised record of dated impact craters has been analyzed for periodicity, and compared with the record of extinctions over the past 260 Myr. A digital circular spectral analysis of 37 crater ages (ranging in age from 15 to 254 Myr ago) yielded evidence for a significant 25.8 ± 0.6 Myr cycle. Using the same method, we found a significant 27.0 ± 0.7 Myr cycle in the dates of the eight recognized marine extinction events over the same period. The cycles detected in impacts and extinctions have a similar phase. The impact crater dataset shows 11 apparent peaks in the last 260 Myr, at least 5 of which correlate closely with significant extinction peaks. These results suggest that the hypothesis of periodic impacts and extinction events is still viable.

This idea is not new and I remembered Stephen Jay Gould's essay "The Cosmic Dance of Siva" (in The Flamingos's Smile) which describes one of the early such hypothesis followed by his trademark meditations of the role of paleontology in understanding the nature of evolution and the history of life. Gould was always irked by the opinions held by many that paleontology is a dusty sort of a science, where people spend their careers fighting over species names, and that they have nothing important to say about the theoretical aspects of evolution. A large part of his popular science writing effort was devoted to demolishing this notion. He was very successful in it with essay after essay beautifully demonstrating the utmost importance of paleontology in highlighting life's little oddities as well as its grand patterns.

Paleontology in the early 1970's underwent something of a change in attitude. Decades before "big data" became a buzzword, researchers led by David Raup, Jack Sepkoski, Leigh Van Valen and Tom Schopf, to name a few, began amassing enormous data sets on fossil characteristics and species distributions and subjected them to rigorous statistical analysis in an effort to elucidate distribution of biodiversity and macro-evolutionary trends. Gould's own work was substantial. Ideas such as "punctuated equilibrium" (with Niles Eldridge) which relies on the fossil record to tease out patterns in the mode and tempo of evolution, were met with admiration as well as fierce criticism as was his thinking on the role of contingency and chance and the limits of natural selection and adaptive evolution as explanations for life's historical trajectories. His theoretical forays did make paleontologists think more broadly about their data and what it tells us about evolution but my take is that it didn't cause a revolution in evolutionary theory as was made out by the media and by Gould's rhetoric. But he did elevate the status of paleontology and that can only be good for science.

He writes:

Most hot ideas turn out to be wrong. I can only hope that I will not be remembered as the man who campaigned with a name for the nonexistent (surely worse than a moon for the misbegotten). Some chances are certainly worth taking. If Thalia smiles and Siva exists, think what it all will mean for my beloved science of paleontology. We have labored so long under the onus of boredom and dullness. We are guardians of life's history, but we are often depicted as mindless philatelists of stone; specialists in tiny corners of space, time, and taxonomy; purveyors of such arcane names as Pharkidonotus percarinatus in extended orgies of irrelevant detail. The editors of Britain's leading scientific journal wrote of us in 1969: "Scientists in general might be excused for assuming that most geologists are paleontologists and most paleontologists have staked out a square mile as their life's work."

That impression has changed since to include paleontology as an important contributor to evolutionary theory. For that, the field owes him a debt.

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ABOUT THIS BLOG

I am a Sedimentary Geologist. On Rapid Uplift I write mostly about topics within the geosciences, but sometimes on biological evolution and environmental issues. I like to travel and in my free time I teach 12 year old kids soccer and rugby.